Rotating machines have been a traditional source of both supply power for ringing telephones and tones for signaling to a subscriber on the progress of a call. These machines included a battery driven DC motor connected to an AC alternator.
Now, however, modern semiconductor technology has been applied in this area to develop completely static ringing and tone generation devices. Power inverters, energized from a DC source, generate 20 Hz ringing signals, while oscillators and amplifiers generate the various tone signals. The inverters employ transistors or thyristors as well as step-up transformers to convert the direct current supplied from a battery to an alternating current ringing signal.
In order to avoid the use of magnetic core transformers and other inductive elements, static energy storage devices such as capacitors have been employed to perform basic energy conversion functions. Capacitor circuits provide DC-AC conversion via polarity reversal, step-up, and step-down functions, for example. An arrangement utilizing a capacitor circuit is shown in U.S. Pat. No. 3,553,479 issued to D. Nelson on Jan. 5, 1971. However, known arrangements such as the one shown in U.S. Pat. No. 3,553,479 require the use of complex switching apparatus to alter the topology of fthe capacitor circuit during charging and discharging cycles. Generally, these topological alterations include changing the connection of a capacitor circuit from series to parallel and vice versa.